Lithium attenuates the proconvulsant effect of adolescent social isolation stress via involvement of the nitrergic system

Resocialization mitigates depressive behaviors induced by social isolation stress in mice: Attenuation of hippocampal neuroinflammation and nitrite level

BACKGROUND AND AIM

Social isolation stress (SIS) is a stressor known to trigger depressive behaviors. Psychiatric disorders are associated with neurobiological changes, such as neuroinflammation and an increase in nitric oxide (NO) signaling. Despite the well-established detrimental effects of SIS and the involvement of neuroinflammation and NO in depression, potential management strategies, especially resocialization, remain insufficiently explored. Our aim was to elucidate the effects of resocialization on depressive behaviors in socially isolated mice, with a focus on the possible involvement of neuroinflammation and nitrite in the hippocampus (HIP).

METHODS

We utilized 24 Naval Medical Research Institute male mice, maintained under both social and isolation conditions (SC and IC). After the isolation period, the mice were divided into two groups of eight, including the SIS group and a resocialized group. The SC group was kept without exposure to isolation stress. We conducted the open-field test, forced swimming test, and splash test to evaluate depressive behaviors. Additionally, nitrite levels, as well as the gene expression of interleukin (IL)-1β, tumor necrosis factor (TNF), and toll-like receptor 4 (TLR4) in the HIP, were measured.

RESULTS

The study found that resocialization significantly reduces depressive behaviors in SIS mice. The results suggest that the antidepressive effects of resocialization may be partially due to the modulation of the neuroinflammatory response and nitrite levels in the HIP. This is supported by the observed decrease in hippocampal gene expression of IL-1β, TLR4, and TNF, along with a reduction in nitrite levels following resocialization.

CONCLUSION

These insights could pave the way for new management strategies for depression, emphasizing the potential benefits of social interactions.

Unmasking hidden risks: The surprising link between PDE5 inhibitors and seizure susceptibility

BACKGROUND

Phosphodiesterase 5 inhibitors (PDE5i) are the first line treatment for erectile dysfunction; however, several articles and case reports have shown central nervous system effects, that can cause seizures in susceptible patients. This study aims to describe the changes caused by the use of Sildenafil and Tadalafil through the analysis of abnormalities expressed in the electrocorticogram (ECoG) of rats and evaluate the seizure threshold response and treatment of seizures with anticonvulsants.

MATERIALS AND METHODS

The study used 108 rats (Wistar). Before surgery for electrode placement in dura mater, the animals were randomly separated into 3 experiments for electrocorticogram analysis. Experiment 1: ECoG response to using PD5i (Sildenafil 20mg/kg and Tadalafil 2.6mg/kg p.o.). Experiment 2: ECoG response to the use of PD5i in association with Pentylenetetrazole (PTZ-30 mg/kg i.p.), a convulsive model. Experiment 3: ECoG response to anticonvulsant treatment (Phenytoin, Phenobarbital and Diazepam) of seizures induced by association IPDE5 + PTZ. All recordings were made thirty minutes after administration of the medication and analyzed for ten minutes, only once. We considered statistical significance level of *p<0.05, **p<0.01 and ***p < 0.001.

RESULTS

After administration of Sildenafil and Tadalafil, there were increases in the power of recordings in the frequency bands in oscillations in alpha (p = 0.0920) and beta (p = 0.602) when compared to the control group (p<0.001). After the use of Sildenafil and Tadalafil associated with PTZ, greater potency was observed in the recordings during seizures (p<0.001), however, the Sildenafil group showed greater potency when compared to Tadalafil (p<0.05). Phenobarbital and Diazepam showed a better response in controlling discharges triggered by the association between proconvulsant drugs.

CONCLUSIONS

PDE5i altered the ECoG recordings in the rats' motor cortexes, demonstrating cerebral asynchrony and potentiating the action of PTZ. These findings demonstrate that PDE5i can lower the seizure threshold.

Nicorandil Exerts Anticonvulsant Effects in Pentylenetetrazol-Induced Seizures and Maximal-Electroshock-Induced Seizures by Downregulating Excitability in Hippocampal Pyramidal Neurons

N-(2-hydroxyethyl) nicotinamide nitrate (nicorandil), a nitrate that activates adenosine triphosphate (ATP)-sensitive potassium (K_ATP) channels, is generally used in the treatment of angina and offers long-term cardioprotective effects. It has been reported that several K_ATP channel openers can effectively alleviate the symptoms of seizure. The purpose of this study was to investigate the improvement in seizures induced by nicorandil. In this study, seizure tests were used to evaluate the effect of different doses of nicorandil by analysing seizure incidence, including minimal clonic seizure and generalised tonic-clonic seizure. We used a maximal electroshock seizure (MES) model, a metrazol maximal seizure (MMS) model and a chronic pentylenetetrazol (PTZ)-induced seizure model to evaluate the effect of nicorandil in improving seizures. Each mouse in the MES model was given an electric shock, while those in the nicorandil group received 0.5, 1, 2, 3 and 6 mg/kg of nicorandil by intraperitoneal injection, respectively. In the MMS model, the mice in the PTZ group and the nicorandil group were injected subcutaneously with PTZ (90 mg/kg), and the mice in the nicorandil group were injected intraperitoneally with 1, 3 and 5 mg/kg nicorandil, respectively. In the chronic PTZ-induced seizure model, the mice in the PTZ group and the nicorandil group were injected intraperitoneally with PTZ (40 mg/kg), and the mice in the nicorandil group were each given 1 and 3 mg/kg of PTZ at a volume of 200 nL. Brain slices containing the hippocampus were prepared, and cell-attached recording was used to record the spontaneous firing of pyramidal neurons in the hippocampal CA1 region. Nicorandil (i.p.) significantly increased both the maximum electroconvulsive protection rate in the MES model and the seizure latency in the MMS model. Nicorandil infused directly onto the hippocampal CA1 region via an implanted cannula relieved symptoms in chronic PTZ-induced seizures. The excitability of pyramidal neurons in the hippocampal CA1 region of the mice was significantly increased after both the acute and chronic administration of PTZ. To a certain extent, nicorandil reversed the increase in both firing frequency and proportion of burst spikes caused by PTZ (P < 0.05). Our results suggest that nicorandil functions by downregulating the excitability of pyramidal neurons in the hippocampal CA1 region of mice and is a potential candidate for the treatment of seizures.

Ellagic acid through attenuation of neuro-inflammatory response exerted antidepressant-like effects in socially isolated mice

Recent studies have been demonstrated that neuroinflammation plays a crucial role in the pathophysiology of depression. Therefore, anti-inflammatory medications could be regarded as a potentially effective treatments for depression. Ellagic acid (EA) is a natural polyphenol with antioxidant and anti-inflammatory properties. This study aimed to evaluate the antidepressant-like effect of EA in a mouse model of social isolation stress (SIS), considering its potential anti-neuroinflammatory properties. In this study, 48 male mice were divided into six groups (n = 8), including saline-treated control (socially conditioned (SC)) group and SIS (isolation conditioned (IC)) groups treated with saline or EA at doses of 12.5, 25, 50, and 100 mg/kg, respectively. Saline and EA were administrated intraperitoneally for 14 constant days. Immobility time in the forced swimming test (FST) and grooming activity time in the splash test were measured. The gene expression of inflammatory cytokines relevant to neuroinflammation was assessed in the hippocampus by real-time PCR. Results showed that SIS significantly increased immobility time in the FST and reduced grooming activity time in the splash test. In addition, the expression of inflammatory genes, including TNF-α, IL-1β, and TLR4 increased in IC mice's hippocampi. Findings showed that EA decreased immobility time in the FST and increased grooming activity time in the splash test. Moreover, EA attenuated neuroimmune-response in the hippocampus. In conclusion, finding determined that EA, through attenuation of neuroinflammation in the hippocampus, partially at least, exerted an antidepressant-like effect in the mouse model of SIS.

Tiagabine suppresses pentylenetetrazole-induced seizures in mice and improves behavioral and cognitive parameters by modulating BDNF/TrkB expression and neuroinflammatory markers

Tiagabine (Tia), a new-generation antiseizure drug that mimics the GABAergic signaling by inhibiting GABA transporter type-1, is the least studied molecule in chronic epilepsy models with comorbid neurobehavioral and neuroinflammatory parameters. Therefore, the current study investigated the effects of Tia in a real-time manner on electroencephalographic (EEG) activity, behavioral manifestations and mRNA expression in pentylenetetrazole (PTZ)-kindled mice. Male BALB/c mice were treated with tiagabine (0.5, 1 and 2 mg/kg) for 21 days with simultaneous PTZ (40 mg/kg) injection every other day for a total of 11 injections and monitored for seizure progression with synchronized validation through EEG recordings from cortical electrodes. The post-kindling protection from anxiety and memory deficit was verified by a battery of behavioral experiments. Isolated brains were evaluated for oxidative alterations and real-time changes in mRNA expression for BDNF/TrkB, GAT-1 and GAT-3 as well as neuroinflammatory markers. Experimental results revealed that Tia at the dose of 2 mg/kg maximally inhibited the development of full bloom seizure and reduced epileptic spike discharges from the cortex. Furthermore, Tia dose-dependently exerted the anxiolytic effects and protected from PTZ-evoked cognitive impairment. Tia reduced lipid peroxidation and increased superoxide dismutase and glutathione levels in the brain via augmentation of GABAergic modulation. PTZ-induced upregulated BDNF/TrkB signaling and pro-inflammatory cytokines were mitigated by Tia with upregulation of GAT-1 and GAT-3 transporters in whole brains. In conclusion, the observed effects of Tia might have resulted from reduced oxidative stress, BDNF/TrkB modulation and mitigated neuroinflammatory markers expression leading to reduced epileptogenesis and improved epilepsy-related neuropsychiatric effects.

Implication of nitrergic system in the anticonvulsant effects of ferulic acid in pentylenetetrazole-induced seizures in male mice

OBJECTIVES

Seizures are abnormal discharge of neurons in the brain. Ferulic acid (FA) is a phenolic compound with antioxidant and neuroprotective effects. The present study aimed to investigate the role of the nitrergic system in the anticonvulsant effect of FA in pentylenetetrazol (PTZ)-induced seizures in male mice.

METHODS

64 male Naval Medical Research Institute (NMRI) mice weighing 25-29 g were randomly divided into eight experimental groups (n=8). FA at doses 5, 10, and 40 mg/kg alone and in combination with L-nitro-arginine methyl ester (L-NAME) (nitric oxide synthase inhibitor) or L-arginine (L-arg) (nitric oxide [NO] precursor) was administrated (intraperitoneal). PTZ was injected (i.v. route) 30 min after drugs administration (1 mL/min). Seizure onset time was recorded and the nitrite levels of prefrontal cortex and serum were determined by the Griess method.

RESULTS

FA at doses of 10 and 40 mg/kg significantly increased the seizure threshold as well as reduced the serum and brain NO levels in comparison to the saline-received group. Co-administration of the effective dose of FA (10 mg/kg) plus L-arg significantly decreased the seizure threshold in comparison to the effective dose of FA alone. Co-injection of the sub-effective dose of FA (5 mg/kg) with L-NAME significantly increased the seizure threshold as well as significantly decreased the brain NO level in comparison to the sub-effective dose of FA alone.

CONCLUSIONS

We showed that the nitrergic system, partially at least, mediated the anticonvulsant effect of FA in PTZ-induced seizures in mice. We concluded that L-NAME potentiated while L-arg attenuated the anticonvulsant effect of FA.

What is the Role of Lithium in Epilepsy?

Lithium is a well-known FDA-approved treatment for bipolar and mood disorders. Lithium has been an enigmatic drug with multifaceted actions involving various neurotransmitters and intricate cell signalling cascades. Recent studies highlight the neuroprotective and neurotrophic actions of lithium in amyotrophic lateral sclerosis, Alzheimer's disease, intracerebral hemorrhage, and epilepsy. Of note, lithium holds a significant interest in epilepsy, where the past reports expose its non-specific proconvulsant action, followed lately by numerous studies for anti-convulsant action. However, the exact mechanism of action of lithium for any of its effects is still largely unknown. The present review integrates findings from several reports and provides detailed possible mechanisms of how a single molecule exhibits marked pro-epileptogenic as well as anti-convulsant action. This review also provides clarity regarding the safety of lithium therapy in epileptic patients.

Posible involvement of nitric oxide in anticonvulsant effects of citicoline on pentylenetetrazole and electroshock induced seizures in mice

Cerebroneurovascular trauma is recognized as an important risk factor in the development of seizure and epilepsy. Administration of citicoline in these situations is a conventional therapeutic strategy, which combines neurovascular protection and repair effects. The aim of the present study is clarifying the effect of acute and sub-chronic citicoline administration on pentylenetetrazole (PTZ) and electroshock induced seizures in mice. Besides we examined the probable role of NO and its interaction with citicoline in seizure experiments.

Male mice were received acute and sub-chronic regimens of different doses of citicoline (62.5, 125, 250 and 500 mg/kg) before the intravenous or intraperitoneal PTZ-induced seizures or electroshock. To clarify the probable role of NO, 7-nitroindazole (7-NI) (60 mg/kg) or aminoguanidine (AG) (100 mg/kg) were injected 5 min before citicoline in separate groups.

The results revealed that neither acute nor sub-chronic treatment with citicoline could affect the seizures induced by intravenous or intraperitoneal PTZ, but in electroshock model, citicoline showed anti-epileptic properties. Co-administration of citicoline and selective nitric oxide synthase (NOS) inhibitors amplified the anticonvulsant effect of citicoline.

The current results indicated that citicoline has anticonvulsant effects probably through the inhibition of NO.

Implication of NMDA-NO pathway in the antidepressant-like effect of ellagic acid in male mice

Depression is one the common psychiatric disorders through the world. Nitric oxide (NO) and N-methyl-d-aspartate receptor (NMDA-R) are involved in the pathophysiology of depression. Previous studies have been reported various pharmacological properties for ellagic acid (EA). We aimed to evaluate possible involvement of NMDA-NO pathway in the antidepressant-like effect of EA. To do this, we used relevant behavioral tests to evaluate depressive-like behavior. In order to find effective and sub-effective doses of agents, mice treated with EA (6.25, 12.5, 25, 50 and 100 mg/kg), L-NAME (5 and 10 mg/kg), L-arg (25 and 50 mg/kg), NMDA (75 and 150 mg/kg) and ketamine (0.25 and 0.5 mg/kg). Furthermore, mice were treated with combination of sub-effective dose of EA plus sub-effective doses of L-NAME and/or ketamine as well as treated with effective dose of EA in combination of effective doses of L-arg and/or NMDA. Level of NO and gene expression of NR2A and NR2B subunits of NMDA-R were assessed in the hippocampus. Results showed that EA dose dependently provoked antidepressant-like effects and also decreased the hippocampal NO level as well as expression of NMDA-Rs. Co-administration of sub-effective doses of L-NAME or ketamine with sub-effective dose of EA potentiated the effect of EA on behaviors, NO level as well as NMDA-Rs gene expression in the hippocampus. However, co-treatment of effective dose of EA with effective doses of L-arg or NMDA mitigated effects of EA. In conclusion, our data suggested that NMDA-NO, partially at least, are involved in the antidepressant-like effect of EA.

Nitric oxide and glutamate are contributors of anti-seizure activity of rubidium chloride: A comparison with lithium

The neuro-protective effects of rubidium and lithium as alkali metals have been reported for different central nervous system dysfunctions including mania and depression. The aim of this study was evaluating as well as comparing the effects of rubidium chloride (RbCl) and lithium chloride (LiCl) on different seizures paradigms in mice and determining the involvement of NMDA receptors and nitrergic pathway. To assess the seizures threshold, animals received intravenous pentylenetetrazole (PTZ, 0.5%; 1 mL/min). Male NMRI mice (6-8 weeks) received intraperitoneal (i.p.) injections of different doses of RbCl and LiCl. Doses greater than 10 mg/kg of RbCl showed a significant anticonvulsant activity 60 min after administration; the anticonvulsant effects of LiCl was observed at the doses more than 5 mg/kg and after 30 min in PTZ-induced seizure threshold. But, RbCl (10, 20 mg/kg, i.p) or LiCl (5, 10 mg/kg, i.p) injection did not induce protection against maximal electroshock (MES) or intraperitoneal injection of PTZ lethal dose (80 mg/kg)-induced seizure models. Pre-treatment with L-NAME (non-selective nitric oxide synthase (NOS) inhibitor, 10 mg/kg; i.p.) and 7-nitroindazole (selective neuronal NOS inhibitor, 30 mg/kg; i.p.) enhanced the anticonvulsive effects of both RbCl (5 mg/kg, i.p.) and LiCl (1 mg/kg, i.p.) in PTZ-induced seizure threshold model. Injection of MK-801 (NMDA receptor antagonist, 0.05 mg/kg; i.p.) before RbCl (5 mg/kg, i.p.; P < 0.001) and LiCl (1 mg/kg, i.p.; P < 0.001) administration increased the anti-seizure activity. But, treatment with L-arginine (precursor of nitric oxide, 100 mg/kg; i.p.) decreased the seizure threshold of both RbCl (20 mg/kg, i.p.; P < 0.001) and LiCl (10 mg/kg, i.p.; P < 0.001). Measurement of nitrite levels in hippocampus of animals revealed a remarkable reduction after treatment with RbCl (20 mg/kg, i.p; P < 0.05) and LiCl (10 mg/kg, i.p; P < 0.01). To conclude, rubidium may protect central nervous system against seizures in PTZ-induced seizures threshold model through NMDA/nitrergic pathways with a similarity to lithium effects in mice.

Involvement of opioid system in behavioral despair induced by social isolation stress in mice

Social isolation stress (SIS) as a type of chronic stress could induce depressive- and anxiety-like behaviors. Our study evaluates the role of opioid system on negative behavioral impacts of SIS in male NMRI mice. We investigated effects of morphine, a nonselective opioid receptor (OR) agonist, naltrexone (NLX), an OR antagonist, naltrindole (NLT), a delta opioid receptor (DOR) antagonist, SNC80, a DOR agonist, U-69593, a kappa opioid receptor (KOR) agonist, nor-Binaltorphimine, a selective KOR antagonist and cyprodime hydrochloride a selective mu opioid receptor (MOR) antagonist on depressive- and anxiety-like behaviors. Using RT-PCR we evaluated ORs gene expression in mice brain. Our findings showed that SIS induced anxiety- and depressive-like behavior in the forced swimming test, open field test, splash test and hole-board test. Moreover, administration of SNC-80 significantly mitigated anxiety- and depressive-like behaviors. NLT decreased grooming-activity in the splash test. Excitingly, administration of agents affecting KOR failed to alter the negative effects of SIS. RT-PCR demonstrated that MOR and KOR gene expression decreased in socially isolated mice; however, SIS did not affect DORs expression. Our findings suggest that SIS at least in part, probably via altering endogenous opioids particularly MORs and KORs but not DORs mediated negative impacts on behavior; also, it could be concluded that DORs might be considered as a novel target for studying depression and anxiety.

Anticonvulsant effect of minocycline on pentylenetetrazole-induced seizure in mice: involvement of nitric oxide and N-methyl-d-aspartate receptor

Anticonvulsant effects of minocycline have been explored recently. This study was designed to examine the anticonvulsant effect of acute administration of minocycline on pentylenetetrazole-induced seizures in mouse considering the possible role of the nitric oxide/N-methyl-d-aspartate (NMDA) pathway. We induced seizure using intravenous administration of pentylenetetrazole. Our results showed that acute administration of minocycline increased the seizure threshold. Furthermore, co-administration of subeffective doses of the nonselective nitric oxide synthase (NOS) inhibitor NG-l-arginine methyl ester (10 mg/kg) and the neuronal NOS inhibitor 7-nitroindazole (40 mg/kg) enhanced the anticonvulsant effect of subeffective doses of minocycline (40 mg/kg). We found that inducible NOS inhibitor aminoguanidine (100 mg/kg) had no effect on the antiseizure effect of minocycline. Moreover, l-arginine (60 mg/kg), as a NOS substrate, reduced the anticonvulsant effect of minocycline. We also demonstrated that pretreatment with the NMDA receptor antagonists ketamine (0.5 mg/kg) and MK-801 (0.05 mg/kg) increased the anticonvulsant effect of subeffective doses of minocycline. Results showed that minocycline significantly decreased the hippocampal nitrite level. Furthermore, co-administration of a neuronal NOS inhibitor like NMDA receptor antagonists augmented the effect of minocycline on the hippocampal nitrite level. In conclusion, we revealed that anticonvulsant effect of minocycline might be, at least in part, due to a decline in constitutive hippocampal nitric oxide activity as well as inhibition of NMDA receptors.

Oxytocin mitigated the depressive-like behaviors of maternal separation stress through modulating mitochondrial function and neuroinflammation

Mother-infant contact has a critical role on brain development and behavior. Experiencing early-life adversities (such as maternal separation stress or MS in rodents) results in adaptations of neurotransmission systems, which may subsequently increase the risk of depression symptoms later in life. In this study, we show that Oxytocin (OT) exerted antioxidant and anti-inflammatory properties. Previous studies indicate that neuroinflammation and mitochondrial dysfunction are associated with the pathophysiology of depression. To investigate the antidepressant-like effects of OT, we applied MS paradigm (as a valid animal model of depression) to male mice at postnatal day (PND) 2 to PND 14 (3h daily, 9AM to 12AM) and investigated the depressive-like behaviors of these animals at PND 60 in different groups. Animals in this work were divided into 4 experimental groups: 1) saline-treated, 2) OT-treated, 3) atosiban (OT antagonist)-treated and, 4) OT+ atosiban-treated mice. We used forced swimming test (FST), splash test, sucrose preference test (SPT) and open field test (OFT) for behavioral assessment. Additionally, we used another set of animals to investigate the effects of MS and different treatments on mitochondrial function and the expression of the relevant genes for neuroinflammation. Our results showed that MS provoked depressive- like behaviors in the FST, SPT and splash test. In addition, our molecular findings revealed that MS is capable of inducing abnormal mitochondrial function and immune-inflammatory response in the hippocampus. Further, we observed that treating stressed animals with OT (intracerebroventricular, i.c.v. injection) attenuated the MS-induced depressive-like behaviors through improving mitochondrial function and decreasing the hippocampal expression of immune-inflammatory genes. In conclusion, we showed that MS-induced depressive-like behaviors in adult male mice are associated with abnormal mitochondrial function and immune-inflammatory responses in the hippocampus, and activation of OTergic system has protective effects against negative effects of MS on brain and behavior of animals.